Biodegradable plastics

Abstract

A method for producing biodegradable plastic from natural materials containing polysaccharides by treating the polysaccharide-containing materials with a basic aqueous solution, subsequently treating the mixture with a modifying material that converts pendant hydroxyl groups at any carbon atom of the anhydroglucose units of the saccharide to create polysaccharide carboxylate, and then reacting the product with proteins to produce a biodegradable copolymer with electrostatic chemical bonds between protein and polysaccharide carboxylate molecules. The process provides relatively inexpensive methods for preparing biodegradable plastics that are useful for manufacturing various articles.

1. A method for the preparation of biodegradable plastics, said method consisting essentially of:
 (I) providing a suspension in a basic aqueous carrier of a finely divided natural material containing a saccharide selected from the group consisting of
 (i) polysaccharides, 
 (ii) oligosaccharides, and 
 (iii) a combination of (i) and (ii); 
 
 (II) adding water to the suspension; 
 (III) agitating the suspension for a period of time; 
 (IV) subjecting the product resulting from step (III) to a modifying material that converts any pendant hydroxyl group at any carbon atom of the anhydroglucose unit of the saccharide to a carboxylate, thereby forming a polysaccharide carboxylate, without breaking carbon—carbon bonds that form the ring of the anhydroglucose units of the saccharides, such modification selected from the group consisting of:
 (A) acylation using a material selected from the group consisting of cyclic anhydrides selected from the group consisting of
 (i) maleic anhydride, 
 (ii) succinic anhydride, 
 (iii) glutaric anhydride, 
 (iv) phthalic anhydride and, 
 (v) derivatives of (i), (ii), (iii), and (iv); 
 
 (B) carboxymethylation using materials selected from the group consisting of:
 (i) haloalkanoic acids and 
 (ii) salts of haloalkanoic acids, and, 
 
 (C) oxidation using an oxidizing agent selected from the group consisting of:
 (a) hypochlorites; 
 (b) hydrogen peroxide; 
 (c) ozone and air, to provide a solid anionic material wherein pendant hydroxyl groups on any carbon atom of the anhydroglucose units of the saccharides are carboxylated and the carbon—carbon bonds that form the ring of the anhydroglucose units of the saccharide are not broken, and thereafter, 
 
 
 (V) combining the material resulting from (IV) with a protein and allowing the resulting material and the protein to react with each other by forming interpolymeric electrostatic bonds between the protein and polysaccharide carboxylate molecules without the formation of strong, interpolymeric covalent bonds between the protein and polysaccharide molecules. 
 
     
     
       2. A plastic prepared by the method of  claim 1 . 
     
     
       3. A method as claimed in  claim 1  wherein the natural material is selected from the group consisting of:
 (i) starchy materials 
 (ii) cellulosic materials, 
 (iii) lignocellulosic materials, 
 (iv) hemicellulosic materials, 
 (v) plant gum containing materials, 
 (vi) polysaccharide-containing materials and, 
 (vii) oligosaccharide-containing materials. 
 
     
     
       4. A method as claimed in  claim 1  wherein the natural material is selected from the group consisting of: 
       
         
           
                 
                 
                 
               
                     
                 
                   (i) plant tubers 
                   (ii) wheat 
                   (iii) seeds 
                 
                   (iv) shells of seeds 
                   (v) stems 
                   (vi) roots 
                 
                   (vii) leaves of plants 
                   (vi) fruit 
                   (vii) fruit skins 
                 
                   (viii) wood 
                   (ix) tree branches 
                   (x) tree bark 
                 
                   (xi) straw 
                   (xii) grass 
                   (xiii) distiller dry grain 
                 
                   (xiv) sugar beet pulp 
                   (xv) cellulose pulp 
                   (xvi) paper waste 
                 
                   (xvii) cotton 
                   (xviii) linen 
                   (xix) vegetables 
                 
                   (xx) vegetable skins. 
                 
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
       5. A method as claimed in  claim 1  wherein the protein is selected from the group consisting of: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   (i) soy protein isolate, 
                   (ii) casein separated from milk, 
                 
                     
                   (iii) casein dispersed in milk, 
                   (iv) whey protein isolate, 
                 
                     
                   (v) whey protein, 
                   (vi) potato protein, 
                 
                     
                   (vii) ovalbumin, 
                   (viii) animal albumins, 
                 
                     
                   (ix) blood protein, and 
                   (x) molasses raffinate. 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
               
            
           
         
       
     
     
       6. A method of preparing a moldable biodegradable plastic containing a coploymer of a polysaccharide and a protein through electrostatic bonding and not covalent bonding comprising:
 a. forming a dispersion of fine particles of at least one polysaccharide in a basic pH aqueous solution, 
 b. converting pendant hydroxyl groups on carbon atoms of the anhydroglucose unit of the polysaccharide to polysaccharide carboxylate groups at a sufficiently low temperature and absence of chemicals such that the carbon—carbon bonds that form the ring of the anhydroglucose units of the polysaccharide are not broken, and 
 c. reacting the material from step b while at a basic pH with a protein in the absence of a reducing agent for said protein to form said moldable biodegradable plastic copolymer. 
 
     
     
       7. The method of  claim 6  for the preparation of molded biodegradable plastics, said method consisting essentially of:
 (I) providing a suspension in a basic aqueous carrier of a finely divided natural material containing a saccharide selected from the group consisting of
 (i) polysaccharides, 
 (ii) oligosaccharides, and 
 (iii) a combination of (i) and (ii); 
 
 (II) adding water to the suspension; 
 (III) agitating the suspension for a period of time; 
 (IV) subjecting the product resulting from step (III) to a modifying material that converts pendant hydroxyl groups at any carbon atom of the anhydroglucose unit of the saccharide to carboxylates, thereby forming polysaccharide carboxylates without breaking carbon—carbon bonds that form the ring of the anhydroglucose units of the saccharides, such modification selected from the group consisting of:
 (A) acylation using a material selected from the group consisting of cyclic anhydrides selected from the group consisting of
 (i) maleic anhydride, 
 (ii) succinic anhydride, 
 (iii)glutaric anhydride, 
 (iv) phthalic anhydride and, 
 (v) derivatives of (i), (ii), (iii), and (iv); 
 
 (B) carboxymethylation using materials selected from the group consisting of:
 (i) haloalkanoic acids and 
 (ii) salts of haloalkanoic acids, and, 
 
 (C) oxidation using an oxidizing agent selected from the group consisting of:
 (a) hypochlorites; 
 (b) hydrogen peroxide; 
 (c) ozone and 
 (d) air, to provide a solid anionic material wherein pendant hydroxy groups on any carbon atom of the anhydroglucose units of the saccharides are carboxylated and the carbon—carbon bonds that form the ring of the anhydroglucose units of the saccharide are not broken, and thereafter, 
 
 
 (V) combining the material resulting from (IV) with a protein and allowing the resulting material and the protein to react with each other by forming interpolymeric electrostatic bonds between the protein and the polysaccharide carboxylate molecules without the formation of strong, interpolymeric covalent bonds between protein and polysaccharide molecules, 
 (VI) thereafter molding the product from (V), and 
 (VII) thereafter drying the molded product. 
 
     
     
       8. A plastic prepared by the method of  claim 7 . 
     
     
       9. The method as claimed in  claim 6  wherein step a. of the method is carried out at room temperature. 
     
     
       10. The method as claimed in  claim 7  wherein step III of the method is carried out at room temperature. 
     
     
       11. A method for the preparation of molded biodegradable plastics, said method of consisting essentially of:
 (I) providing a suspension in a basic aqueous carrier of a finely divided natural material containing a saccharide selected from the group consisting of:
 (i) polysaccharides, 
 (ii) oligosaccharides, and 
 (iii) a combination of (i) and (ii); 
 
 (II) adding water to the suspension; 
 (III) agitating the suspension for a period of time; 
 (IV) subjecting the product resulting from step (III) to a modifying material that converts pendant hydroxyl groups at any carbon atom of the anhydroglucose unit of the saccharide to carboxylates, thereby forming polysaccharide carboxylates without breaking carbon—carbon bonds that form the ring of the anhydroglucose units of the saccharides, such modification selected from the group consisting of:
 (A) acylation using a material selected from the group consisting of cyclic anhydrides selected from the group consisting of 
 (i) maleic anhydride, 
 (ii) succinic anhydride, 
 (iii) glutaric anhydride, 
 (iv) phthalic anhydride and, 
 (v) derivatives of (i), (ii), (iii), and (iv); 
 (B) carboxymethylation using materials selected from the group consisting of: 
 (i) haloalkanoic acids and 
 (ii) salts of haloalkanoic acids, and, 
 (C) oxidation using an oxidizing agent selected from the group consisting of:
 (a) hypochlorites; 
 (b) hydrogen peroxide; 
 (c) ozone and 
 (d) air, to provide a solid anionic material wherein pendant hydroxy groups on any carbon atom of the anhydroglucose units of the saccharides are carboxylated and the carbon—carbon bonds that form the ring of the anhydroglucose units of the saccharide are not broken, and thereafter, 
 
 
 (V) combining the material resulting from (IV) with a protein and allowing the resulting material and the protein to react with each other by forming interpolymeric electrostatic bonds between protein and polysaccharide carboxylate molecules without the formation of strong, interpolymeric covalent bonds between protein and polysaccharide molecules, 
 VI thereafter reducing the amount of water in (V) and, 
 (VII) thereafter molding the product from (VI), and 
 (VIII ) thereafter drying the molded product from (VII). 
 
     
     
       12. A plastic prepared by the method of  claim 11 . 
     
     
       13. The method as claimed in  claim 11  wherein step III of the method is carried out at room temperature.